Wanderer wrote in message . ..
On Wed, 10 Sep 2003 15:21:57 +0100, Roland Perry wrote:

In message , Wanderer
writes
Finally! Confirmation that the two faults were indeed related. As some
of us insisted (against solid opposition) from the start.

Not quite true. You conveniently snipped the *real* reason, which was
almost certainly human error.

The *reason* for the second outage might have been human error [1], but
the second outage was most definitely *caused* (ie triggered) by the
first. It wasn't an "unrelated" incident.

On any interconnected system, the National Grid being a prime example,
events are by definition related. This incident was caused by a
classic very simple installation 'cock-up' made 2 years ago and not
discovered or exposed since; system design, configuration and incident
response were correct and supplies would have been securely maintained
otherwise.

The second outage (Wimbledon - New Cross 275kV circuit No.2) which
caused the loss of supply was a 'phantom' overload trip, there was no
equipment fault and total load was 33% of line rating. Overload
detection relays, connected via 1,200:1 transformer, are rated 1Amp or
5Amp with a wide ranging multiplier, 5A was specified but 1A installed
and through all the checks nobody spotted the error. This meant that
tripping was initiated (time delay involved, irrelevant here) at 23%
of rating and 20% of correct overload setting, so in the past 2 years
this line can't have loaded above that level even at peak winter
demand indicating the generous level of redunancy provided.

It's accepted that when the system is being reconfigured, as it was
after the first, potentially explosive, fault warning; there can be 5
to 10 mins 'switching time' when supply is via a single circuit. The
risk of a second fault on that circuit during this time is estimated
at 1:40,000 though that doesn't apply here with the system wrongly
set-up. The engineers planning the switching could not have known the
line would trip.

[1] Although you could argue that it was really caused by failure to
implement a procedure that would have noticed and rectified that human
error.

Yes. Knowing the very strict and thorough commisioning and testing
procedures that once were enforced, one is left wondering whether
corners have been cut since privatisation.

They were carried out but I guess those engineers assumed they had
been handed over correctly installed equipment and never thought to
check the relay rating, pity they aren't brightly colour coded.
Simulating real life faults is simply not possible or wise.

Reading the full report my impression is of a well run and financed
operation not obviously damaged by privatisation with London area
investment running at £50m pa. Ironically the duplicate circuit,
Wimbledon - New Cross No.1, is out from 1/7 to 28/9 for upgrade and
refurb.

Lessons have been, painfully, learnt and the relay error is not likely
to happen again. All 45,000 are being checked (none found after
9,000). I would say the system is now secure, building extra lines
would be very expensive. The LT loss of supply is rather laid on EDF,
the London distribution operator, who chose to operate their Wimbledon
132kV Substation in a way that resulted in LT and others losing supply
when the Grid was able to maintain the full load without interuption,
and should have reconnected LT in a couple of mins at most. I get the
impression there was only one engineer in their Control who didn't
know what hit him...

Source:
http://image.guardian.co.uk/sys-file...on28082003.pdf

On 10 Sep 2003 15:31:14 -0700, robsignals
wrote in :
detection relays, connected via 1,200:1 transformer, are rated 1Amp or
5Amp with a wide ranging multiplier, 5A was specified but 1A installed

....

They were carried out but I guess those engineers assumed they had
been handed over correctly installed equipment and never thought to
check the relay rating, pity they aren't brightly colour coded.

Given that there appear to be only two different ratings, an obvious
question is, "Why not?"

--
Ivan Reid, Electronic & Computer Engineering, ___ CMS Collaboration,
Brunel University. Room 40-1-B12, CERN
KotPT -- "for stupidity above and beyond the call of duty".

On Thu, 11 Sep 2003 09:48:26 +0000 (UTC), "Dr Ivan D. Reid"
wrote:

On 10 Sep 2003 15:31:14 -0700, robsignals
wrote in :
detection relays, connected via 1,200:1 transformer, are rated 1Amp or
5Amp with a wide ranging multiplier, 5A was specified but 1A installed

...

They were carried out but I guess those engineers assumed they had
been handed over correctly installed equipment and never thought to
check the relay rating, pity they aren't brightly colour coded.

Given that there appear to be only two different ratings, an obvious
question is, "Why not?"

becuase some pratt would probabably colour them red & green them
employe colour blind engineers.
--
This post does not reflect the opinions of all saggy cloth
cats be they a bit loose at the seams or not
GSX600F - Matilda the (now) two eared teapot, complete with
white gaffer tape, though no rectal chainsaw

"Dr Ivan D. Reid" wrote in message
...
On 10 Sep 2003 15:31:14 -0700, robsignals
wrote in :
detection relays, connected via 1,200:1 transformer, are rated 1Amp or
5Amp with a wide ranging multiplier, 5A was specified but 1A installed

...

They were carried out but I guess those engineers assumed they had
been handed over correctly installed equipment and never thought to
check the relay rating, pity they aren't brightly colour coded.

Given that there appear to be only two different ratings, an obvious
question is, "Why not?"

The cost of producing the item? Perhaps they aren't made?

You'd hope that the maintenance engineers actually bothered to read things.
Perhaps if the correct colour code was yellow they might stuff a banana in
by mistake.

W K wrote:
"Dr Ivan D. Reid" wrote in message
...
On 10 Sep 2003 15:31:14 -0700, robsignals
wrote in :

detection relays, connected via 1,200:1 transformer, are rated 1Amp or
5Amp with a wide ranging multiplier, 5A was specified but 1A installed

They were carried out but I guess those engineers assumed they had
been handed over correctly installed equipment and never thought to
check the relay rating, pity they aren't brightly colour coded.

Given that there appear to be only two different ratings, an obvious
question is, "Why not?"


The cost of producing the item? Perhaps they aren't made?

You'd hope that the maintenance engineers actually bothered to read things.
Perhaps if the correct colour code was yellow they might stuff a banana in
by mistake.

The company my late father worked for made various control
components for applications such as petrochemical plants,
nuclear power-stations, oil-refineries etc. The components
were colour-coded as to their intended use/ratings.

On one occasion, the wrong component got fitted, which
caused a major shutdown which then resulted in a significant
lawsuit [this was in the USA back in the 1970s].

"It should have been made obvious by colour-coding that
the wrong unit was fitted" said the refinery-company's
lawyers.

"The units are colour-coded according to use and rating"
my father's company replied.

"The fitter who fitted it is colour-blind" admitted the
refinery operators after some days of the trial.

Oops!

-PeteL.

robsignals said:

...I guess those engineers assumed they had been handed over
correctly installed equipment and never thought to check the
relay rating, pity they aren't brightly colour coded. Simulating
real life faults is simply not possible or wise.

Faults don't seem to be the issue. If the line went into overload
protection at a fraction of what it should have done, a simple test
of the line during commissioning (at 50% of rating) would have shown
this.

--
=============================================

Chris Game chrisgame@!yahoo!dotcodotuk
=============================================

PJML said:

"The fitter who fitted it is colour-blind" admitted the
refinery operators after some days of the trial.

A classic - and one of the things quality auditors are trained to
look out for.

--
=============================================

Chris Game chrisgame@!yahoo!dotcodotuk
=============================================

robsignals said:

The risk of a second fault on that circuit during this time is
estimated at 1:40,000 though that doesn't apply here with the
system wrongly set-up.

You mean that was the calculated failure probablity ignoring the
protection system?

Some of this seems fairly elementary - I know this is easy to say
with hindsight - but are the electricity supplies really this badly
managed?

--
=============================================

Chris Game chrisgame@!yahoo!dotcodotuk
=============================================

On 10 Sep 2003 15:31:14 -0700, robsignals wrote:

Wanderer wrote in message . ..

snip

On any interconnected system, the National Grid being a prime example,
events are by definition related.

Bad choice of words on your part, I think.How can a lightning strike in
the west country and a 3rd party cable damage that happened to occur at
more or less the same time in the west midland be related? No, that may
never have happened, but I give it as an example of the flaw in your
argument.

This incident was caused by a
classic very simple installation 'cock-up' made 2 years ago and not
discovered or exposed since; system design, configuration and incident
response were correct and supplies would have been securely maintained
otherwise.

Not true. Somewhere between design, configuration and commisioning a
current multiplier was wrongly set, and was not picked up by testing
procedures that should have picked it up.

snipped the actual details, read with interest, but there seem to be
some notable gaps that raise even more questions [1]

Yes. Knowing the very strict and thorough commisioning and testing
procedures that once were enforced, one is left wondering whether
corners have been cut since privatisation.

They were carried out but I guess those engineers assumed they had
been handed over correctly installed equipment and never thought to
check the relay rating, pity they aren't brightly colour coded.
Simulating real life faults is simply not possible or wise.

Paragraph 177 in the report is quite explicit about the procedures used
to commission the protection. I would not fault them as written.
Certainly the responsibility for returning a circuit to commision in
good and proper order rests *exclusively* with the guys carrying out the
work.

Reading the full report my impression is of a well run and financed
operation not obviously damaged by privatisation with London area
investment running at £50m pa. Ironically the duplicate circuit,
Wimbledon - New Cross No.1, is out from 1/7 to 28/9 for upgrade and
refurb.

Lessons have been, painfully, learnt and the relay error is not likely
to happen again. All 45,000 are being checked (none found after
9,000). I would say the system is now secure

I don't share your confidence. The report paints a picture of a calm and
ordered working environment that almost certainly did exist two or three
decades ago. I suspect those working for NGT might have some difficulty
in recognising this environment today.

building extra lines
would be very expensive. The LT loss of supply is rather laid on EDF,
the London distribution operator, who chose to operate their Wimbledon
132kV Substation in a way that resulted in LT and others losing supply
when the Grid was able to maintain the full load without interuption,
and should have reconnected LT in a couple of mins at most. I get the
impression there was only one engineer in their Control who didn't
know what hit him...

Unlikely if they operate a centralised control system. But.....

[1] The gaps:-

It would have been nice to see an actual schematic of the network at
Hurst s/s. They have three supergrid t/frs on site. I'm guessing that
each would almost certainly be independently controlled, and
consequently capable of isolation, by circuit breakers on the hv and lv
sides of the t/fr.

Buchholz alarms are usually t/fr specific in the control room, so why
did the NG control engineer apparently disconect the incoming circuit
and not isolate the tranformer indicating the alarm? If this had
happened the overload situation would not have occured.

It would also be interesting to compare areas of responsibility and
manning levels for this part of their network now and say 25 years ago.
What level of authority and/or delegation of that authority holds today
compared to 25 years ago?

On Thu, 11 Sep 2003 13:06:53 +0100, Chris Game wrote:

robsignals said:

The risk of a second fault on that circuit during this time is
estimated at 1:40,000 though that doesn't apply here with the
system wrongly set-up.

You mean that was the calculated failure probablity ignoring the
protection system?

Some of this seems fairly elementary - I know this is easy to say
with hindsight - but are the electricity supplies really this badly
managed?

No, they're exceptionally well managed, as it happens. What seems to
have happened here is that somewhere along the line, someone either
mis-set a relay or failed to notice that a relay had been mis-set. The
procedure for checking that relay appears to be well-written.